Disposable diaper and method for incorporation of elastic member into such diaper

ABSTRACT

A disposable diaper provided with elastic members respectively comprising a plurality of rubber strings in respective side flaps of the diaper so that these elastic members provide a plurality of longitudinally extending elastic lines in said side flaps to provide a good fit of said side flaps around infant&#39;s thighs.

This is a continuation of application Ser. No. 460,909, filed Jan. 23,1983, now abandoned and the benefits of 35 USC 120 are claimed relativeto it.

BACKGROUND OF THE INVENTION

The present invention relates to disposable diaper and a method forincorporation of elastic members into such diaper. More particularly,the present invention relates to a construction of elastic membersfunctioning to fit both side flaps of the disposable diaper of underpanttype around infant's thighs and a method to incorporate such elasticmembers into said diaper.

The elastic members functioning to fit both side flaps of the disposablediaper around infant's thighs has already been adopted by the well knowndisposable diapers of underpant type and the most typical one of suchdiapers of prior art has been disclosed by U.S. Pat. No. 3,860,003.Usually, a single rubber tape has been incorporated into each side flapof the diaper as the elastic member. However, the diaper incorporatedwith such elastic members of single rubber tape type exerts a localizedor linear high pressure around infant's thighs with linear pressuremarks remaining around infant's thighs and sometimes causes a pain forthe infant who wears such diaper particularly when the infant wears thisfor a relatively long period.

To eliminate such drawback, it has already been proposed to use therubber tape which is formed relatively wide, as said elastic member.However, use of the rubber tape formed in such manner would bedisadvantageous in the following aspect.

In view of the molding technique, it is difficult to obtain a rubbertape substantially thinner than the rubber tape which has usually beenused as said elastic member and it would be almost impossible to obtainthe rubber tape of uniform thickness even if molding of extremely thinrubber tape is possible. Accordingly, if the conventional rubber tapeused as the elastic member is formed wider and incorporated into thediaper at the stretching ratio similar to that as used with theconventional rubber tape, a pressure around infant's thighs would beexcessive, since the tensile stress thereof is too high. To obtain anelastic member having a tensile stress which is regarded optimal for apressure to be exerted around infant's thigh, therefore, it is necessaryto reduce the stretching ratio of said elastic member by a quantitycorresponding to an increased width of said elastic member. This wouldresult in an increase of cost due to an additional quantity of materialfor the elastic member required to enlarge the width thereof as well asdue to an additional quantity of material for said elastic memberrequired to reduce the stretching ratio thereof. Such increased cost isseriously disadvantageous for the disposable diaper which should bemanufactured at a reasonably low cost.

It is certainly possible to overcome this drawback when several finerubber strings are used as the elastic member, as will be understoodfrom reading a further later description on the present invention.However, such a measure confronts a difficulty, namely, the disposablediaper must be mass-produced at a low cost and the rubber strings mustbe secured, by means of adhesive, to a backsheet comprising plastic filmor the like and/or to a topsheet comprising nonwoven fabric or the like,both sheets being constituent members of the diaper. Furthermore, saiddrawback can be effectively overcome only when said rubber strings usedas the elastic member are substantially finer than the rubber tapeconventionally used as said elastic member of the diaper. However, finerthe rubber strings to be used as the elastic member are and more thenumber of these rubber strings is, more difficult the handling of theserubber strings for securing them to said sheet(s) by means of adhesiveand the operational efficiency is inevitably reduced.

An object of the present invention is, therefore, to provide an improveddisposable diaper provided with elastic members respectively comprisingseveral rubber strings substantially finer the rubber tapesconventionally used as the elastic members of the disposable diaper andarranged at appropriate intervals in parallel within side flaps of thediaper so as to form several elastically stretchable lines in therespective side flaps and thereby to make good fit of said side flapsaround infant's thighs.

Another object of the present invention is to provide an improveddisposable diaper in which a plurality of extremely fine rubber stringsarranged at appropriate intervals in parallel are used as the elasticmembers as previously mentioned so that the stretching ratio of theserubber strings may be increased while the length of these rubber stringsto be used may be reduced with respect to the conventional rubber tapescommonly used as the elastic members in the disposable diapers of priorart and, as a result, the quantity of rubber material used for theseelastic members may be sufficiently reduced to achieve production of thediaper at a low cost.

Still another object of the present invention is to provide an improvedmethod for incorporation of said plurality of rubber strings serving asthe elastic members into associated components of the disposable diapercomprising steps of continuously feeding these rubber strings,particularly, those in the form of respective single rubber tapes heldby apparent side-by-side joints each having an intrinsic separability tosaid associated components while separating them neatly into apredetermined number of rubber strings, and then securing these rubberstrings to said components by adhesive so that the desired incorporationof these rubber strings into the diaper may be achieved at a highefficiency.

The other objects of the present invention will be apparent from thefollowing description of the invention.

SUMMARY OF THE INVENTION

According to the present invention, there is provided an improvement inthe disposable diaper including a topsheet, a backsheet, an absorbentbody fixedly interposed between said both sheets and elastic membersarranged in respective side flaps formed by portions of said both sheetsextending beyond opposite outer edges of said absorbent body so as to beclosely laid upon one another so that longitudinal elastic lines areformed in said side flaps to fit said side flaps around infant's thighs,said elastic members respectively comprising three (3) to forty-five(45) rubber strings each having a cross-sectional area of 0.03 mm² to0.45 mm² and totally having a cross-sectional area of 0.09 mm² to 1.35mm², being stretched at a stretching ratio of 100% to 400% andsimultaneously secured by adhesive within the respective side flaps atappropriate intervals in parallel so that three (3) to forty-five (45)elastic lines may be formed in said respective side flaps for good fitof these side flaps around infant's thighs There is provided also, inaccordance with the present invention, an improved method forincorporation of these elastic members into said diaper.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a developed plan view showing, partially broken away, anembodiment of the disposable diaper constructed according to the presentinvention;

FIG. 2 is a sectional view taken along the centre line of the diaper asshown by FIG. 1;

FIGS. 3(A) and (B) is a partial perspective view generally showing theelastic members of particular cross sections which can be used within ascope of the present invention;

FIG. 4 is a partial perspective view showing an embodiment of theelastic member which can be used for execution of the method accordingto the present invention;

FIG. 5 is a schematic side view partially showing an apparatus forproduction of the disposable diaper according to the present invention;

FIG. 6 is a plan view showing a dividing station for the elastic memberin the apparatus as shown by FIG. 5;

FIG. 7 is a schematic perspective view showing a mechanical station foradhesive fixation of the elastic members to the diaper;

FIG. 8 is a perspective view showing a nozzle serving for application ofadhesive to the elastic members;

FIG. 9 is a developed perspective view of said nozzle as shown by FIG.8;

FIG. 10 is a sectional view taken along the centre line of the nozzle asshown by FIG. 8; and

FIGS. 11 and 12 are diagrams showing characteristic curves exhibitedwhen a single rubber tape is used and when a group of several rubberstrings is used as each of the elastic members, respectively.

PREFERRED EMBODIMENTS OF THE INVENTION

Preferred embodiments of the present invention will be described inreference with the accompanying drawing.

Referring to FIGS. 1 and 2, a disposable diaper includes a waterpermeable topsheet 11 of nonwoven fabric or the like, a waterimpermeable backsheet 12 of plastic film or the like, an absorbent body13 of fluffed wood pulp or the like, and elastic members 15 arrangedwithin respective side flaps 14 formed by portions of the both sheets11, 12 extending beyond opposite outer edges of the absorbent body 13 soas to be closely laid upon one another so that said elastic members 15be elastically stretchable in the longitudinal direction. Such diaper 10is, when attaching this to an infant, assembled by adhesively connectingpressure-sensitive fastening tapes which have previously been attachedto opposite ends of one waist portion 17 to corresponding opposite endsof the other waist portion 18. The elastic members 15 respectivelycomprise a plurality of rubber strings according to the presentinvention, as will be described later more in detail, and the disposablediaper having the above-mentioned construction in which each elasticmember comprises a single rubber tape is well known from, for example,said U.S Pat. No. 3,860,003.

Although FIGS. 1 and 2 show the diaper 10 having the elastic members 15respectively comprising parallelly spaced three rubber strings 15A inthe respective side flaps 14, it is also possible within the scope ofthe present invention to use the elastic members 15 respectivelycomprising three (3) to forty-five (45) rubber strings each having across-sectional area of 0.03 mm² to 0.45 mm² and totally having across-sectional area of 0.09 mm² to 1.35 mm² parallelly spaced one fromanother in the respective side flaps 14. These rubber strings 15A may beof uniform cross-sectional area or, in some cases, certain strings amongthem may be of different cross-sectional area. In the latter case, itwill be reasonable that the rubber strings 15A of relatively smallcross-sectional area are arranged on the inner side within therespective side flaps 14 and the rubber strings 15A of relatively largecross-sectional area are arranged on the outer side within therespective side flaps 14. However, the elastic members 15 of the formertype are preferably used for execution of the method according to thepresent invention which will be described later. In the diaper 10according to the present invention using such elastic members 15respectively comprising three (3) to forty-five (45) rubber strings 15Ain the respective side flaps 14, there are provided in the respectiveside flaps 14 three (3) to forty-five (45) elastically stretchable lineswhich function to fit the side flaps around infant's thighs. Therespective rubber strings 15A may have circular, elliptical or squarecross-sections. Further, a plurality of rubber string elements 15a maybe integrally joined side-by-side in parallel so as to form each rubberstring 15A having a combined cross-section as shown by FIGS. 3(A) or3(B). The rubber strings 15A each having such combined cross-sectioncorresponding to a plurality of circles joined to one another may beobtained by, for example, molding the respective rubber string elements15a and then by fusing them together before they are sufficiently cooledto be solidified.

When a plurality of rubber strings 15A are used as each of the elasticmembers 15, the tensile stress is reduced and the stretching ratio isincreased in comparison to a single rubber tape used as the elasticmember even when the total cross-sectional area, the material and thestretching ratio of said rubber strings 15A are identical to those ofsaid single rubber tape. And also the tolerable range of unevenstretching ratio is enlarged when said plurality of rubber strings 15Aare used as the elastic member 15. This will be readily understood fromFIGS. 11 and 12 showing result of the experiment conducted by theinventors.

FIG. 11 is a diagram showing characteristic curves exhibited by samplesI, II for comparison when these samples are subjected to a tensilestress (g) varying as given on the ordinate with a stretching ratio (%)varying as given on the abscissa. The sample I comprises a single rubbertape of natural rubber which is 100 mm long, 6.6 mm wide and 0.2 mmthick while the sample II comprises three separate rubber tapes each ofwhich is equally 3.2 mm wide. To generate a tensile stress of 130 g ineach elastic member which has been found to provide the optimal pressurearound infant's thigh, for example, the sample I can be stretched asslightly as by approximately 120% while the sample II can be tolerablystretched as extensively as by approximately 170%.

FIG. 12 is a schematic diagram corresponding to the partially enlargedFIG. 11, showing the tolerable range of uneven stretching ratios for therespective samples I, II when these samples I, II were incorporated intothe associated diapers with the tensile stress of 130 g±10 g asrequirement for the diaper design. Concerning the tolerable range ofuneven stretching ratio, the experimental result indicated approximately27% for the sample I and 34% for the sample II. The tolerable range ofuneven stretching ratio for the sample II is thus larger than that forthe sample I, so that such construction of the sample II facilitates adraft adjustment of the elastic member on a step of its draftingtreatment during execution of the method according to the presentinvention

As seen from such result of the experiment conducted by the inventors,use of a plurality of rubber strings 15A as the elastic member 15corresponding to a single rubber tape divided into several rubber tapesallows a stretching ratio higher than the case in which said singlerubber tape is used as said elastic member to be adopted to obtain adesired pressure around infant's thigh, since the tensile stress islower in the former case than in the latter case. In other words, thelength of the elastic member 15 may be economically reduced. Inconsequence, the diaper according to the present invention in which aplurality of rubber strings 15A are used as the elastic member 15, aquantity of material to be used for the elastic member 15 is reduced incomparison with the diaper of prior art in which a single rubber tape isusually used as each of the elastic members 15 and each diaper can bemanufactured at the correspondingly reduced cost.

The rubber strings 15A serving as the elastic member have their tensilestress lowered as the number thereof increases, so that acorrespondingly higher stretching ratio may be used to increase saidadvantage. However, study by the inventors has shown that, with eachelastic member comprising three (3) to forty-five (45) natural rubberstrings of 0.03 mm² to 0.45 mm² in individual cross-sectional area andof 0.09 mm² to 1.35 mm² in total cross-sectional area, the tensilestress thereof sharply increases when the stretching ratio thereofexcesses 400%, and as a result, a pressure mark clearly remains aroundinfant's thigh. Accordingly, for the diaper according to the presentinvention, the respective elastic members 15 are subjected to a draftingeffect when these elastic members are incorporated into the diaper sothat a stretching ratio of 100% to 400%, preferably of 150% to 350%,more preferably of 250% to 300%, may be attained. At a stretching ratiolower than 100%, a quantity of rubber material to be used should beuneconomically increased. It should be noted here that a single rubbertape, for example, 0.20 mm thick and 6.6 mm wide has usually been usedas such elastic member, wherein said single rubber tape has usually beensubjected to a drafting effect at a stretching ratio of 70% to 100% whenthis single rubber tape is incorporated into each side flap of thediaper. The expression "stretching ratio of 100%" is used here toindicate the case in which the elastic member having its initial lengthof 100 mm was stretched until a length of 200 mm is attained.

Into the disposable diaper constructed according to the presentinvention a plurality of rubber strings 15A each of a relatively smallcross-sectional area are incorporated as the elastic member 15 inparallel at side-by-side spacings, so that the apparent width of therespective elastic members in the associated side flaps (as indicated byW in FIG. 2) is enlarged with respect to the case in which a singlerubber tape is used as the elastic member as in the diaper of prior artand a pressure around infant's thigh is correspondingly reduced. Inconsequence, a pain for the infants often suffer from wearing the diaperof prior art as well as a pressure mark appearing on infant's thigh as aresult of wearing such diaper of prior art are substantially eliminatedby the diaper constructed in accordance with the present invention. Toachieve such effect, although it depends more or less uponcharacteristics such as rigidity of the topsheet 11, the backsheet 12and the absorbent body 13 which are components of the diaper, aplurality of rubber strings 15A used as the respective elastic members15 are arranged within ranges preferably 10 mm to 35 mm and morepreferably 15 mm to 20 mm wide outwardly from the respective outer edgesof the absorbent body.

During use of the diaper constructed according to the present invention,the elastic members 15 respectively comprising a plurality of rubberstrings 15A function as if these elastic members 15 are respectivelyintegrated pieces but they are really separated into the individualrubber strings 15A, respectively, so that these rubber strings 15A areindependently stretched and contracted to facilitate the desired fitaround infant's thighs. The fact that the elastic members 15 are reallyseparated into a plurality of rubber strings 15A is advantageous tomaintain a proper air-permeability in the regions of these elasticmembers 15.

FIG. 4 shows an embodiment of the elastic member 15 to be used forexecution of the method according to the present invention. The elasticmember 15 comprises six rubber strings 15A substantially same in theirsquare cross-sections and these rubber strings 15A are maintained in theform of a single tape by provisional side-by-side joints but haveintrinsic separability from one another. Such joints 20 of theindividual rubber strings 15A are lines which may be bonded by fusion orprovisional joints which may be provided by spraying powder such as talconto the individual rubber strings 15A immediately after these rubberstrings have been molded to prevent these rubber strings from stickingto the other objects and bringing these rubber strings into lightcontact with one another. Said powder clinging to the respective rubberstrings 15A may be removed, if necessary, in actual use of these rubberstrings 15A. Further, said provisional joints 20 may be easily torn offby a slight force laterally exerted thereon and said rubber strings 15Amay be neatly separated along said provisional joints 20. Suchprovisionally joined assembly of six (6) to ninety (90) individualrubber strings 15A may be used as the elastic members 15, since three(3) to forty-five (45) rubber strings 15A are incorporated into eachside flap 14 of the diaper 10 according to the present invention aspreviously described. The assembly of thus provisionally joined rubberstrings is manufactured by Rondex Co., Ltd. (Kohoku-Ku, Yokohama, Japan)and commercially available under the trade name "RONDEX".

FIGS. 5 through 7 schematically illustrate an apparatus for execution ofthe method according to the present invention. This apparatus comprisesa feeding station A, a drafting station B, a separating station C and anapplying station E, respectively, of the elastic members 15.

The feeding station A includes a storage container 21, a guide ring 22and a pair of guide rolls 23, 24, respectively, of the elastic members15 to be introduced from said feeding station A to the drafting stationB.

The drafting station B includes a pair of squeezing rolls 25, 25,another pair of squeezing rolls 26, 26 of a circumferential velocityhigher than that of said pair of squeezing rolls 25, 25, a pair ofcleaning rolls 27, 27 and a beating roll 30, these last-mentioned twocomponents being arranged between said first pair of squeezing rolls 25,25 and said second pair of squeezing rolls 26, 26, and said beating roll30 being provided with several rods 29 extending between opposite endplates 28 to which the respective ends of said rods 29 are fixed alongthe circumferences of the respective end plates 28 at circumferentiallyequal intervals. Each elastic member 15 is subjected to a draftingeffect at a desired stretching ratio between said two pairs of squeezingrolls 25, 25 and 26, 26 while the previously mentioned powder clingingto the elastic member 15 is removed by the pair of cleaning rolls 27,and then the elastic member 15 is beaten by the beating roll 30. Aquantity of powder thus removed by the cleaning rolls from the elasticmember 15 is recovered by suction means or the like arranged adjacentsaid pair of cleaning rolls 27 into a reservoir (not shown). Althoughthe elastic member 15 which can be treated by the apparatus as shown byFIGS. 5 through 7 is not limited to that of the art as shown by FIG. 4,description will be made with respect to the embodiment of the elasticmember 15 as shown by FIG. 4, for convenience of explanation. Theelastic member 15 comprising six (6) rubber strings 15A provisionallyjoined in parallel as previously mentioned is now divided into twoblocks, i.e., an upper block 15A₂ and a lower block 15A₁ which arerespectively guided along upper and lower sides of the beating roll 30interposed between these two blocks 15A₁, 15A₂. The elastic member 15 isdrafted by the second pair of squeezing rolls 26, 26 as said elasticmember 15 is guided along said beating roll 30 and thereby successivelydivided into the respective blocks 15A₁, 15A₂. Simultaneously, thebeating roll 30 functions to beat these blocks 15A₁, 15A₂ so that theseblocks may be easily separated in the separating station C further intothe individual rubber strings 15A, and then introduced into saidseparating station C.

The separating station C includes pairs of squeezing rolls 31, 31, otherpairs of squeezing rolls 32, 32, guide rods 34, 35, 36 arranged atdifferent levels and guide rolls 37, 38, 39, associated with said guiderods 34, 35, 36, respectively, between said pairs of squeezing rolls 31,31 and said pairs of squeezing rolls 32, 32. The respective blocks 15A₁,15A₂ are separated into the individual rubber strings 15A. The firstrubber string 15A of each block is put against the guide rod 34 and thenthe upper side of the guide roll 37, the second rubber string 15A is putagainst the guide rod 35 and then the upper side of the guide roll 38,and the third rubber string 15A is put against the guide rod 36 and thenthe upper side of the guide roll 39. The respective blocks 15A₁, 15A₂thus suspended on the associated guide rods and guide rolls are guidedbetween the pairs of squeezing rolls 32, 32 while these blocks aremaintained in said stretched state and thereby the respective blocks15A₁, 15A₂ are successively separated into the individual rubber strings15A as already mentioned under the tearing effect by said guide rods 34,35, 36 and said guide rolls 37, 38, 39. Thus these individual rubberstrings 15A are introduced into the applying station E.

The applying station E includes guide rolls 41 provided on theperipheral surfaces with a plurality of grooves 40 (FIG. 7), nozzlemeans 42 and a chilling roll 43. There are provided in the vicinity ofthe applying station E a pressure roll 44, a pair of squeezing rolls 45,45, a supply roll 46 serving to support plastic film 12 for thebacksheet of diaper wound therearound, a supply roll 47 serving tosupport nonwoven fabric 11 for the topsheet of diaper wound therearound,a guide roll 48, a conveyor 49 serving to convey the absorbent body 13of diaper, guide rolls 50, 51 and the others. The individual rubberstrings 15A are guided by the associated guide rolls 41 along thegrooves 40 formed therearound and pass by the associated nozzle means 42by which said individual rubber strings 15A are applied with adhesive ofhot melt type and simultaneously regulated with respect to the intervalsat which said individual rubber strings 15A are to be arranged on theassociated side flaps of diaper. The individual rubber strings 15A arecontinuously sticked, while maintained in said stretched state, to theupper surface of the plastic film 12 along opposite side zones thereof,said plastic film 12 being continuously introduced onto the upper sideof the chilling roll 43, and the latter functions also to chill saidadhesive and thereby to solidify it. As seen from FIG. 7, the nonwovenfabric 11 is introduced by the guide roll 48 onto the upper side of saidplastic film 12 while the respective absorbent bodies 13 which havepreviously been formed are conveyed by the conveyor 49 longitudinally atregular intervals into a gap between said nonwoven fabric 11 and saidplastic film 12 so as to be held therebetween. The nonwoven fabric 11and the plastic film 12 are applied by separate nozzle means (not shown)arranged at desired positions with adhesive of hot melt type on theirinner sides before these nonwoven fabric 11 and plastic film 12 are laidupon one another, and then joined so that said absorbent bodies 13 aresecured at regular intervals as above mentioned. Continuous pieces ofdiaper 52 is now pressed by the pressure roll 44 and transferred to thesubsequent process (not shown) in which said continuous diaper 52 willbe cut into individual diaper 10 as shown by FIG. 1.

FIGS. 8 through 10 illustrate an embodiment of said nozzle means 42. Thenozzle means 42 comprises a triangular prism-like first member 53, aplate-like second member 54 and a plate-like third member 55. The firstmember 53 includes an inlet hole 56 opening at the centre of one sidewall, distribution channel 57 communicating with said inlet hole 56 andextending longitudinally of said first member 53, a plurality of jetorifices 59 communicating with said distribution channel 57 and opening,at regular intervals, into an elongate recess 58 formed longitudinallyin another side wall, and a plurality of slits 60 formed at regularintervals in one end of said first member 53. The second member 54includes a plurality of triangular slits 61 at the same intervals assaid slits 60 in one end of said second member 54. The third member 55also includes a plurality of slits 62 at the same intervals as saidslits 60 in one end of said third member 55. The first member 53, thesecond member 54 and the third member 55 are united into complete nozzlemeans 42 when screws 64 are threaded into corresponding threaded holesformed in these three members. The nozzle means 42 of such constructionis arranged in a path of three rubber strings 15A as each elastic member15 between said guide roll 41 and said chilling roll 43 as seen in FIG.5 so that slots 65 respectively comprising said slits 60, 61, 62 aredirected downwards. A reservoir (not shown) adapted to control orregulate supply, blocking and metering of adhesive of hot melt type isconnected with the inlet hole 56. When passing through the respectiveslots 65, the respective three rubber strings 15A as each elastic member15 are applied with said adhesive of hot melt type supplied from saidreservoir through said inlet hole 56, said distribution channel 57, saidjet orifices 59 and said elongate recess 58 to the respective slots 65and sprayed these slots 65. An excessive quantity of said adhesive ofhot melt type which has not been applied on the elastic member 15 isrecovered into a reservoir (not shown) placed under the nozzle means 42.

It is preferred that the elastic member 15 is applied with a properquantity of said adhesive of hot melt type at a proper temperature. Theexperiment conducted by the inventors indicated that the alreadymentioned natural rubber strings 15A each having a cross-sectional areaof approximately 0.185 mm² supplied from said Rondex Co., Ltd. under thetrade name "RONDEX 3SR" is one of preferred products to be used as theelastic member 15. When this particular product is used as material forthe elastic member 15, a preferable quantity of said adhesive of hotmelt type to be applied on one of such rubber strings 15A is 0.1 to 0.2g/m and a preferred temperature for application is a temperature lowerthan 165° C. A quantity of application smaller than 0.1 g/m, in thiscase, would prevent the elastic members 15 from being reliably stickedto the side flaps 14 of the diaper 10 while a quantity more than 0.2 g/mwould cause exudation of said adhesive through the topsheet 12 of thediaper 10, discomfort for the wearer after solidified, and increase ofthe manufacturing cost. Said temperature for application being 165° C.or higher would result in deterioration or even breakage of the rubberstrings 15A. It has been found also that, as said adhesive of hot melttype, such adhesive which is commercially available in our country underthe trade name "KANEBO NSC MQ-975" and presents its viscosity of 120,000cps and 220,000 cps at the temperature of 120° C. and 150° C.,respectively is one of preferred products.

The number of the slots 65 depends on the number of the rubber strings15A to be parallelly arranged in the respective side flaps 14 of thediaper 10. The intervals at which the respective slots 65 are arrangedfunction to regulate the intervals at which the rubber strings 15A areparallelly arranged in the respective side flaps 14 of the diaper 10.

Although the method according to the present invention has beendescribed hereinbefore in reference with FIGS. 5 through 7 showing theapparatus for execution of the inventive method, in which each elasticmember 15 comprising a desired number of rubber strings 15A joined inparallel one another is divided into two blocks 15A₁, 15A₂ while theserubber strings 15A are stretched and then these two blocks 15A₁, 15A₂are further separated into the individual rubber strings 15A,respectively, the other manners as following are also covered by thescope of the method according to the present invention:

(a) the elastic member 15 comprising a desired number of rubber strings15A parallelly joined one to another are separated into the individualrubber strings 15A while said elastic member 15 is placed under adrafting effect;

(b) the elastic member 15 comprising a desired number of rubber strings15A parallelly joined one to another is divided into two blocks 15A₁,15A₂ after stretched, and then these two blocks 15A₁, 15A₂ are furtherseparated into the individual rubber strings 15A; and

(c) the elastic member 15 comprising a desired number of rubber strings15A parallelly joined one to another is separated into the individualrubber strings 15A after stretched.

Apparatuses adapted for execution of these manners (a) through (c) arenot shown but may be readily designed by those skilled in the art inreference with the apparatus as shown by FIGS. 5 through 7.

The elastic member 15 comprising a plurality of rubber strings 15provisionally joined in parallel one to another is used according to theinventive method, as already mentioned, so that said individual rubberstrings 15A are free from entanglement or breakage during treatments insaid supplying station A and drafting station B. Further, the rubberstrings 15A have their intervals regulated by the respective slots 65 ofthe nozzle means 42 and are applied therearound with adhesive so thateach elastic member 15 may be reliably secured in each side flap 14 ofthe diaper 10. Accordingly, the method according to the presentinvention enables the elastic members 15 to be efficiently incorporatedinto the diaper 10 even though these elastic members 15 respectivelycomprise a plurality of extremely fine rubber strings 15A.

EXAMPLE

The absorbent body made of fluffy wood pulp having a unit weight of 450g/m² was interposed between the topsheet, 330 mm×450 mm, 35 g/m²consisting of 50 weight % polyester fibre and 50 weight % rayon fibre,and the backsheet, 330 mm×450 mm consisting of 25μ thick polyethylenefilm; these topsheet, backsheet and absorbent body were fixedlyassembled together by means of adhesive agent of hot melt type; and theelastic members were adhesively incorporated into both side flaps formedby the portions of said both sheets which extend outwardly beyond therespective outer edges of said absorbent body and are laid upon oneanother, so as to obtain a complete diaper as shown by FIG. 1. Theelastic members respectively consisted of three natural rubber strings(total cross-sectional area: 1.32 mm²) each of which was 160 mm long,0.2 mm thick and 2.2 mm wide. These three rubber strings were arrangedin parallel at the intervals of 9 mm while they were stretched to alength of 450 mm so that a tensile stress of 130 g is reached. Theseelastic members were applied with adhesive agent of hot melt type at thetemperature of 160° C., in a quantity of 0.2 g/m for each string. Theadhesive agent used herein had a viscosity of 20000 cps/160° C. and asoftening point of 97° C.

As a control product, a diaper in which the number of rubber strings isdifferent from the above mentioned example was made. In this controldiaper, the elastic members respectively comprising a single rubber tapewhich is 195 mm long, 0.2 mm thick and 6.6 mm wide (cross-sectionalarea: 1.32 mm²) were adhesively secured into the respective side flapswhile said elastic members were stretched so that a length of 450 mm maybe obtained with a tensile stress of approximately 130 g.

Said product according to the present invention and said control productwere attached to 100 infants each weighing 5500 to 11000 g and testedwith respect to urine leakage and pressure mark, and the followingresult was obtained.

    ______________________________________                                                  Leakage test                                                                              Pressure mark test                                                No     Slight   Clear   Slight                                                                              No                                              leakage                                                                              leakage  mark    mark  mark                                  ______________________________________                                        Inventive product                                                                         88       12       16    43    41                                  Control product                                                                           83       17       42    37    21                                  ______________________________________                                    

Concerning the quantity of material used for the elastic member, theinitial dimension of 160 mm was necessary for the inventive product toobtain the desired tensile stress while the initial dimension of 195 mmfor the control product to obtain the same tensile stress. It is obviousfrom this result that the product according to the present invention iseconomically advantageous compared to the control product.

What is claimed is:
 1. A method for incorporation of elastic membersinto a disposable diaper including a topsheet, a backsheet, an absorbentbody fixedly interposed between said both sheets, and elastic membersarranged in respective side flaps formed by portions of said both sheetsextending beyond opposite outer edges of said absorbent body so as to beclosely laid upon one another so that longitudinal elastic lines areformed in said side flaps to fit said side flaps around infant's thighs,said method comprising steps of feeding an elastic member in the form ofa tape consisting of six (6) to ninety (90) rubber strings joinedtogether in parallel, said rubber strings each having a substantiallyequal cross-sectional area of 0.03 mm² to 0.45 mm² and a totallycross-sectional area of 0.18 mm² to 2.7 mm², separating these rubberstrings along joints thereof into individual rubber strings whilestretched at a stretching ratio of 100% to 400%, supplying respectivethree (3) to forty-five (45) rubber strings of said six (6) to ninety(90) rubber strings onto regions of the diaper to be formed into saidside flaps at appropriate intervals while these rubber strings areapplied with adhesive agent, and adhesively securing these rubberstrings in said regions.
 2. The method for incorporation of elasticmembers into a disposable diaper according to claim 1, wherein theelastic member comprising six (6) to ninety (90) rubber strings joinedtogether in parallel is divided into two blocks each comprising three(3) to forty-five (45) rubber strings while said elastic member isstretched, and then these two blocks are further separated intoindividual rubber strings.
 3. The method for incorporation of elasticmembers into a disposable diaper according to claim 1, wherein theelastic member is separated into individual rubber strings while saidelastic member comprising six (6) to ninety (90) rubber strings joinedtogether in parallel is stretched.
 4. The method for incorporation ofelastic members into a disposable diaper according to claim 1, whereinthe elastic member comprising six (6) to ninety (90) rubber stringsjoined together in parallel is divided into two blocks each comprisingthree (3) to forty-five (45) after said elastic member is stretched, andthen these two blocks are further separated into individual rubberstrings.
 5. The method for incorporation of elastic members into adisposable diaper according to claim 1, wherein the elastic membercomprising six (6) to ninety (90) rubber strings joined together inparallel is stretched and then separated into individual rubber strings.6. The method for incorporation of elastic members into a disposablediaper according to claim 1, wherein the individually separated rubberstrings are secured in the diaper at intervals regulated by intervals ofnozzle slots through which said adhesive agent is applied onto theindividual rubber strings.
 7. The method for incorporation of elasticmembers into a disposable diaper according to claim 1, wherein theelastic members comprising six (6) to ninety (90) rubber strings havingintrinsic separability but maintained in the form of a single tape byprovisional joints may be neatly separated by a slight tearing forceinto individual rubber strings.